The present invention relates to a propulsion process of buried pipe, and more particularly to a so-called propulsion process for burying an underground pipe such as a sewer without excavating the soil from the ground surface, by forming a burying hole horizontally in the soil from a shaft, and propelling while sequentially burying the pipe in the formed burying hole.
Because the propulsion method is not necessary to excavate the ground widely along the burying route, the propulsion method is intensively researched and developed as a method favorable for the installation site where the traffic volume is large and it is difficult to limit the traffic.
In the general conventional propulsion method, first a shaft is excavated and formed in the ground, and a burying hole in the horizontal direction is formed from the side of this shaft into the ground, by a device called the leader. The burying hole is formed by digging the ground by an earth auger or other digging means attached to the leader, or by compacting the ground at the conical tip portion of the leader, and either method is selected depending on the soil properties and installation conditions.
At the rear part of the leader, a buried pipe cut in a specific length is connected. The buried pipes of specific length are coupled one after another and extended in length. At the rear end of the first buried pipe or the extended buried pipe row, propelling force is applied by a jack installed in the shaft to propel the buried pipe row and the leader, while the burying hole is formed and buried pipe is installed by the leader.
The reason of using buried pipes for specific length in the propulsion process is that the handling length of the buried pipe is limited depending on the space of the shaft in order to propel prefabricated pipes into the burying hole through the shaft. Besides, to transport the pipes from the pipe mill to the site of installation and store them, it is necessary to use pipes of fixed size.
The seam of the buried pipes of specific length is connected by butt-to-butt adhesion of the pipe ends, or fitting the pipe end to the collar. In the case of collar fitting, a water stop rubber is set on the abutting face of the pipe and collar to prevent invasion of ground water.
In such a conventional propulsion process, however, the working of the seam of the pipes is difficult, and the watertightness at the seam is inferior, and the strength is not sufficient.
That is, every time one pipe is propelled into the burying hole, the next pipe must be joined to the preceding pipe, and it takes time until the pipe ends adhere sufficiently, or when fitting by a collar with water stop rubber, it must be handled carefully so as not to damage the rubber, and the work is very complicated and laborious. Since these jobs are manually done in a narrow shaft at the site, the finishing quality differs with the skill of the workers, and the pipe seam may not be joined completely, the water stopping property may not be exhibited fully, or the strength is often lowered.
Besides, in the seam part, since the strength is weaker than that of the pipe main body, and when the propulsion force from the jack or the frictional drag force from the ground is applied while propelling, the seam adhesion may be separated, the collar and the water stop rubber may be separated, or the end of the buried pipe may be broken.
If the seam junction is imperfect, ground water or sand may enter the buried pipe, or the planned water flow of the pipe may not be obtained when used as the sewer, or the water matter flowing in the pipe may lead into the ground to induce pollution problems.
Particularly, in the conventional propulsion process, a propulsion force is applied to the rear end of the buried pipe row, and all the buried pipes and the leader are propelled by this propulsion force, and an extremely large stress is concentrated on the seam of pipes, which leads to various problems as mentioned above.